SQL & PL/SQL

Hi all,

i want to know abt decode function in oracle-sql
i..e passing the parameters in decode using decode using ":" bind parameter

select JOB, decode(:j,'CLERK','MANAGER','ANALYST','EXEC',JOB) FROM EMP;
i declared the j variable in sql environment
VARIABLE J VARCHAR2(20);
i exec the query
and passed as the clerk as input parameter
but iam getting the o/p as
JOB DECODE(:J
--------- ---------
MANAGER MANAGER
MANAGER MANAGER
MANAGER MANAGER
SALESMAN SALESMAN
SALESMAN SALESMAN
SALESMAN SALESMAN
CLERK CLERK
SALESMAN SALESMAN
ANALYST ANALYST
CLERK CLERK
ANALYST ANALYST

JOB DECODE(:J
--------- ---------
CLERK CLERK

12 rows selected.

SQL> PRINT J;

J
--------------------------------------------------------------------------------

im not getting o/p
so please hlelp me only : should be used not &
this is my first thread.
execuse me if any mistakes

tons of thanks in advance to all